# Could anybody help me out designing "Loop stability of flyback SMPS"

#### mishra87

Joined Jan 17, 2016
997
I have been reading so many articles and books of stability design of SMPS.
i understood some basic concepts pole, zero, RPHZ, GM, PM, GCM, PCM.
Types of compensations.

Now could anybody make me understand the cracks of loop stability.
How to choose which types of compensation to be used. ???
How to choose crossover frequency ???
How much GM and PM for a stable system ???
And how do we calculate pole and zero values.

My intention to understand all these things theoretically ????

Thank you so much in Advance !!!

#### crutschow

Joined Mar 14, 2008
32,064
Look at the attached for a start.

#### Attachments

• 384.2 KB Views: 11

#### mishra87

Joined Jan 17, 2016
997
Adding further more in discussion -
Could anybody explain a bit more about below -
Its type two compensation in loop stability -

below is pole zero location

v

Now could anybody explain me below bode plot and how it define loop stability.

#### crutschow

Joined Mar 14, 2008
32,064
In order for the loop to be stable you need phase and gain margin (points where the phase reaches 90° and the gain reaches 0dB).
Here is some information on that.

#### mishra87

Joined Jan 17, 2016
997
In order for the loop to be stable you need phase and gain margin (points where the phase reaches 90° and the gain reaches 0dB).
Here is some information on that.
I dont understand you mentioned "phase reaches 90 deg"

I have studied
PM- point where gain curve crosses 0 db point (from there to Phase curve distance) and that frequency is Gain cross over frequency.
GM- point where phase curve crosses -180 deg (from there to gain curve distance) and that frequency is phase cross over frequency.

#### Attachments

• 89.3 KB Views: 3

#### mishra87

Joined Jan 17, 2016
997
Nowadays receiving a few comment on topic on this group. !!!

#### crutschow

Joined Mar 14, 2008
32,064
I dont understand you mentioned "phase reaches 90 deg"
Yes that should be 180° for the total loop phase shift.